Commit 44abafc4 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller

tcp: disallow cwnd undo when switching congestion control

When the sender switches its congestion control during loss
recovery, if the recovery is spurious then it may incorrectly
revert cwnd and ssthresh to the older values set by a previous
congestion control. Consider a congestion control (like BBR)
that does not use ssthresh and keeps it infinite: the connection
may incorrectly revert cwnd to an infinite value when switching
from BBR to another congestion control.

This patch fixes it by disallowing such cwnd undo operation
upon switching congestion control.  Note that undo_marker
is not reset s.t. the packets that were incorrectly marked
lost would be corrected. We only avoid undoing the cwnd in
Signed-off-by: default avatarYuchung Cheng <>
Signed-off-by: default avatarSoheil Hassas Yeganeh <>
Signed-off-by: default avatarNeal Cardwell <>
Signed-off-by: default avatarEric Dumazet <>
Signed-off-by: default avatarDavid S. Miller <>
parent e7519f99
......@@ -180,6 +180,7 @@ void tcp_init_congestion_control(struct sock *sk)
const struct inet_connection_sock *icsk = inet_csk(sk);
tcp_sk(sk)->prior_ssthresh = 0;
if (icsk->icsk_ca_ops->init)
if (tcp_ca_needs_ecn(sk))
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